In a conventional spark plug, a cylindrical metal shell, a cylindrical insulator fitted in the metal shell and a circular cylindrical center electrode disposed within the insulator are disposed so that their axes are substantially concentrically in a radial direction. In addition, a pillar-like ground electrode has a construction in which the ground electrode is bent at an intermediate portion thereof so as to be formed into an L-shape and a proximal end portion thereof is welded to be joined to a front end portion of the metal shell, while a distal end portion thereof is disposed to be spaced apart in a radial direction from a metal tip (a noble metal tip) which is welded to be joined to a front end portion of the center electrode. As this occurs, a predetermined spark discharge gap is formed between the noble metal tip of the center electrode and the distal end portion of the ground electrode (for example, refer to Patent Document 1).
Incidentally, for a spark plug in which a distal end portion of a ground electrode is disposed to be spaced apart in a radial direction from a noble metal tip of a center electrode, although it is a general producing method that the center electrode and an insulator are assembled after bending and punching operations are performed in advance on the pillar-like ground electrode which is welded to be joined to a front end portion of a metal shell, this method has had a problem that assembling errors are made, which makes it difficult to obtain an accurate spark discharge gap. Consequently, in the related art, the pillar-like ground electrode is bent and punched in slightly larger dimensions, and after the center electrode and the insulator are assembled, the ground electrode is bent to be deformed in a direction in which the ground electrode moves towards or away from the noble metal tip of the center electrode to thereby adjust the spark discharge gap to a suitable distance.